The sd_bus_error structure carries
information about a D-Bus error condition. The functions described
below may be used to set and query fields in this structure. The
name field contains a short identifier
of an error. It should follow the rules for error names described
in the D-Bus specification, subsection Valid
Names. A number of common, standardized error names are
described in
sd-bus-errors(3),
but additional domain-specific errors may be defined by
applications. The message field usually
contains a human readable string describing the details, but might
be NULL. An unset sd_bus_error structure
should have both fields initialized to NULL. Set an error
structure to SD_BUS_ERROR_NULL in order to
reset both fields to NULL. When no longer necessary, resources
held by the sd_bus_errorstructure should
be destroyed with sd_bus_error_free().

sd_bus_error_set() sets an error
structure to the specified name and message strings. The strings
will be copied into internal, newly allocated memory. It is
essential to free the error structure again when it is not
required anymore (see above). The function will return an
errno-like negative value (see errno(3))
determined from the specified error name. Various well-known
D-Bus errors are converted to well-known errno
counterparts, and the other ones to -EIO. See
sd-bus-errors(3)
for a list of well-known error names. Additional error mappings
may be defined with
sd_bus_error_add_map(3). If
e is NULL no error structure is initialized
but the error is still converted into an
errno-style error. If
name is NULL, it is
assumed that no error occurred, and 0 is returned. This means that
this function may be conveniently used in a
return statement. If
message is NULL no message is set. This
call can fail if no memory may be allocated for the name and
message strings, in which case an
SD_BUS_ERROR_NO_MEMORY error might be set
instead and -ENOMEM returned. Do not use this call on error
structures that are already initialized. If you intend to reuse an
error structure free the old data stored in it with
sd_bus_error_free() first.

sd_bus_error_setf() is similar to
sd_bus_error_set(), but takes a printf(3)
format string and corresponding arguments to generate the
message field.

sd_bus_error_set_const() is similar to
sd_bus_error_set(), but the string parameters
are not copied internally, and must hence remain constant and
valid for the lifetime of e. Use this call
to avoid memory allocations when setting error structures. Since
this call does not allocate memory it will not fail with an
out-of-memory condition, as
sd_bus_error_set() can, as described
above. Alternatively, the
SD_BUS_ERROR_MAKE_CONST() macro may be used
to generate a literal, constant bus error structure
on-the-fly.

sd_bus_error_set_errno() will set
name from an
errno-like value that is converted to a D-Bus
error. strerror_r(3)
will be used to set message. Well-known
D-Bus error names will be used for name
if applicable, otherwise a name in the
"System.Error." namespace will be generated. The
sign of the specified error number is ignored. The absolute value
is used implicitly. The call always returns a negative value, for
convenient usage in return statements. This
call might fail due to lack of memory, in which case an
SD_BUS_ERROR_NO_MEMORY error is set instead,
and -ENOMEM returned.

sd_bus_error_set_errnof() is similar to
sd_bus_error_set_errno(), but in addition to
error, takes a printf(3)
format string and corresponding arguments. The
message field will be generated from
format and the arguments.

sd_bus_error_set_errnofv() is similar to
sd_bus_error_set_errnof() but takes the
format string parameters as va_arg(3)
parameter list.

sd_bus_error_get_errno() converts the
name field of an error structure to an
errno-like (positive) value using the same
rules as sd_bus_error_set(). If
e is NULL, 0 will be
returned.

sd_bus_error_copy() will initialize
dst using the values in
e. If the strings in
e were set using
sd_bus_set_error_const(), they will be shared.
Otherwise, they will be copied. Returns a converted
errno-like, negative error code.

sd_bus_error_is_set() will return a
non-zero value if e is
non-NULL and an error has been set,
false otherwise.

sd_bus_error_has_name() will return a
non-zero value if e is
non-NULL and an error with the same
name has been set,
false otherwise.

sd_bus_error_free() will destroy
resources held by e. The parameter itself
will not be deallocated, and must be free(3)d
by the caller if necessary. The function may also be called safely
on unset errors (error structures with both fields set to NULL),
in which case it performs no operation. This call will reset the
error structure after freeing the data, so that all fields are set
to NULL. The structure may be reused afterwards.

The functions sd_bus_error_set(),
sd_bus_error_setf(),
sd_bus_error_set_const(), when successful,
return the negative errno value corresponding to the
name parameter. Functions
sd_bus_error_set_errno(),
sd_bus_error_set_errnof() and
sd_bus_error_set_errnofv(), when successful,
return the negative value of the error
parameter. If an error occurs, one of the negative error values
listed below will be returned.

sd_bus_error_get_errno() returns
false when e is
NULL, and a positive errno value mapped from
e->name otherwise.

sd_bus_error_copy() returns 0 or a
positive integer on success, and a negative error value converted
from the error name otherwise.

sd_bus_error_is_set() returns a
non-zero value when e and the
name field are
non-NULL, zero otherwise.

sd_bus_error_has_name() returns a
non-zero value when e is
non-NULL and the
name field is equal to
name, zero otherwise.

sd_bus_error is not reference
counted. Users should destroy resources held by it by calling
sd_bus_error_free(). Usually error structures
are allocated on the stack or passed in as function parameters,
but they may also be allocated dynamically, in which case it is
the duty of the caller to free(3)
the memory held by the structure itself after freeing its contents
with sd_bus_error_free().